Wireless access networks have become a key element of a variety of telecommunications network environments. As to enterprise network environments, they provide convenient wireless access to network resources for employees or customers carrying laptops and/or mobile handheld devices. In addition, wireless access points operable with diverse communication devices, such as laptops, mobile phones, etc., are broadly used in public environment such as e.g., hotels, train stations, airports, restaurants, schools, universities and homes, and are mostly used to offer high-speed interne access.
The telecommunication industries and operators are currently investigating the possibility to further increase the coverage area offered by cellular communications network systems to home or small areas. Examples of cellular communication network system are: the Universal Mobile Telecommunication Systems (UMTS) network, also known as third generation (3G) cellular network system or wideband code division multiplexing access (WCDMA) network; the Global System for Mobile telecommunications (GSM) network; the General Packet Radio Service (GPRS) network that utilizes the infrastructure of a GSM system; Two further examples of cellular access networks are EDGE and EGPRS which are further enhancements to GSM and GPRS. EDGE refers to enhanced Data rates for GSM Evolution, and EGPRS refers to Enhanced GPRS.
According to such investigation, a limited number of users (e.g. a user equipment (UE)) may be provided with e.g. WCDMA or 3G coverage using a small radio base stations (RBS) also called a “femto RBS” that would be connected to a radio network controller (RNC) of the 3G network using some kind of internet protocol (IP) based transmission. The coverage area so provided is called a “femto cell” to indicate that the coverage area is relatively small compared with an area of a macro cell of a public land mobile network (PLMN). Other terminology for a femto RBS includes a “Home RBS” and/or a “home 3G access point (H3GAP)” and/or a “home access point (HAP)” and/or a “home Node B (HNB)”. It should be mentioned that small cells known as picocells may serve small areas such as part of a building, a street corner or a airplane cabin and are usually smaller than microcells, which in turn is smaller than a macrocell. The picocells are traditionally provided as coverage or capacity extensions and do not include an access control mechanism. This means that all users that are allowed to access macrocells of a PLMN are also allowed to access microcells and picocells of the same PLMN.
One alternative for the IP based transmission is to use fixed broadband access (like xDSL, Cable, etc.) to connect the femto RBS to the RNC. Another alternative would be to use mobile broadband access e.g. some WiMAX technologies or HSDPA and enhanced uplink also known as HSPA.
FIG. 1 illustrates an example of a WCDMA network 1 built with a traditional architecture including one or several RNCs 20 and femto RBSs 40 working as H3GAP. However the RBS's and RNC's may as well be collapsed and form a single node in a so called flat architecture. As shown in FIG. 1, the network 1 comprises a core network (CN) 80 connected to a RNC 20 that controls all radio base stations connected to it, i.e. macro RBS 30 and femto RBSs 40. The macro RBS 30 serves a macro cell 31 whereas a femto RBS 40 serves a femto cell 41. As illustrated, each femto RBS 40 serves its dedicated femto cell 41. As well known in the art, a RBS is typically situated at an interior (e.g. centre) of the respective cell which the RBS serves, but for the sake of clarity, the macro RBS 30 and the femto RBSs 40 of FIG. 1 are shown instead as being associated by double headed arrows to their respective cells. At least some of the femto cells 41 are geographically overlayed or overlapped by the macro cell 31.
A user equipment (UE) 50 communicates with one or more cells or one or more RBSs over a radio interface. The UE 50 can be a mobile phone (or “cellular phone”), a laptop with mobile termination and thus can be e.g. portable, pocket, handheld, computer-included, or car-mounted mobile device which can communicate voice and/or data with a radio access network. The UE 50 may further communicate with the radio access network via a femto RBS 40 through an internet protocol (IP) based transmission network 60 which, as described earlier, can be either broadband fixed IP based transmission (e.g. xDSL) or broadband mobile IP based transmission (e.g. WiMAX or HSPA) or any other suitable IP based transmission.
In the wireless communications network system depicted in FIG. 1, the interface between the each femto RBS 40 and the RNC 20 can be called the extended tub interface “Iub+” which is usually formed by an IP connection over the IP based transmission network 60. In some implementations, the Iub+ resembles the Iub interface between the macro RBS 30 and the RNC 20, but the Iub+ interface is modified for conveying additional information such as the identity of the femto RBS 40 e.g. during the initial power-on procedure of the femto RBS 40.
Also illustrated in FIG. 1, is the Iu interface used between the RNC 20 and the CN 80. Note that in a flat architecture there would not necessarily exist any Iub(+) interface because, as described above, in such flat architecture the RBS and the RNC can form a single node. In order to limit the users of UEs 50 of the femto cell 41 to the ones that are allowed, an access control feature can be implemented in the system. This way, at any UE attempt to camp on the femto cell, it is checked if the user is an allowed user. The international subscriber mobile identity (IMSI) of allowed users (or UEs) per femto RBS are stored in a database 70, known as an access control database (ACDB), to which the stand-alone or integrated RNC has access. This approach is described in the international patent application with publication number WO 2007/136339.
In prior art WCDMA networks that are based on macro/micro/pico cells of a PLMN i.e. WCDMA networks that do not include femto cells, a service area identifier (SAI) is used to identify an area consisting of one or more cells belonging to the same location area (LA). Such an area is called a service area and can be used for indicating the location of a UE to the core network (CN). A SAI of a current cell is indicated by the RNC to the CN when a signalling connection is established for a UE. The CN can use the SAI for the purposes of routing and charging as well as different location based services i.e. services that are based on the current location of the UE. Examples of such services:                Emergency call routing (e.g. to route a call to the correct emergency center)        Location calling services (e.g. to route a call to e.g. the closest taxi)        Legal intercept (to find out UE location on service area basis).        Charging indication (e.g. as charging areas).        
The CN can also be informed about SAI changes for a UE using standard mechanisms in the Iu-interface and in a so called RANAP (Radio Access Network Application Part) protocol signalling over the Iu-interface. In the 3GPP standard (Third Generation Partnership Project), the SAI is defined as consisting of a service area code (SAC) together with the PLMN-id (consisting of a mobile country code (MCC), a mobile network code (MNC)) and the location area code (LAC)). The SAI can be defined according to the following:
SAI=PLMN-id∥LAC∥SAC
The LAI is also defined as consisting of PLMN-id and LAC and therefore SAI can be also defined as follows:
SAI=LAI∥SAC
The SAC is usually defined by the operator of the network and is normally configured in the RNC via O&M (operation and maintenance). The SAI is further set for a macro/micro/pico cell depending on the location of the macro/micro/pico cell. The SAI values are further coordinated between the radio access network and the CN so that e.g. the relevant location based services in the CN can be configured with this information. The RNC includes separately both the LAI and SAI for the current macro/micro/pico cell towards the CN. The LAI is used by the CN for e.g. mobility management (MM purposes) and the SAI can be used for e.g. location based services as previously described.
As described above, a SAI of a macro/micro/pico cell in the network is indicated by the RNC to the CN when a signalling connection is established for a UE. If femto cells are introduced in the network, a SAI for each such femto cell needs to be indicated by the RNC and mapped to, for example, a location information in the CN. With manual (or semi-manual) configuration, a femto cell could be given one or more SAIs and a mapping of these SAI(s) to, for example, a location information in the CN could be performed in a similar way as for the pico, micro and macro cells. However manual (or semi-manual) configuration both in the RNC and in the CN, of a huge number of femto cells e.g. hundred of thousands or even millions of femto cells is not considered a feasible solution especially since SAIs are not broadcasted in the network. In addition, it is normally the end users that install the femto cells on their own, without any intervention from the operator personnel. This means that the femto cell installation, including the selection of one or more SAIs, needs to happen automatically. In such a scenario with the huge number of femto cells, the RNC further needs to indicate all the SAIs to the CN which leads to excessive configuration load in the CN because the CN would be involved in all location based services. In addition to location based services, other services such as differentiated charging may also be offered to different UEs that are allowed to access a femto cell, which require additional identifiers to be defined in the CN. This would increase further the configuration load in the CN as well as in the RNC. In the light of the above problems related to the number of the femto cells, different types of UEs accessing a femto cell and the automatic nature of the installation procedure, a solution is needed that automatically selects the correct SAI for a UE accessing a specific femto cell.